(1) Field of the Invention
The present invention relates to measurement of the degree of erosion of the wall of a material conveying conduit and particularly to the automatic detection of the need to repair or replace a portion of such a conduit or a similar member which is subject to wear. More specifically, this invention is directed to electrical sensors for use in determining the degree of erosion of a surface over which a material, and especially a granular and/or abrasive material, flows. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well-suited for use in monitoring the effects of erosion of a surface. Thus, by way of example, the present invention may find application in fuel pipe elbows through which pulverized coal is delivered to a furnace. There has, in the prior art, been no sensor available which would be suitable for use in an environment as harsh as a coal pipe elbow. Accordingly, it has been prior practice to periodically perform a manual inspection of such conduits in order to determine if the degree of erosive wear has been sufficient to warrant repair. Alternatively, repair/replacement schedules for fuel pipes have been established based upon past history. It would, of course, be highly desirable to avoid the necessity of performing a periodic, time consuming and expensive manual inspection. Observing a maintainence schedule based upon prior history has the obvious disadvantage that premature shut-down for maintenance will typically result. Restated, because of differences in materials which result in an unusually high rate of erosion, a very costly pipe failure could occur unless a very conservative maintenance schedule is adopted.
Surface wear detectors are, of course, well-known in the art. Such detectors have been proposed, and in some cases employed, to provide a warning of a severely worn brake lining. Examples of such brake lining wear detectors may be seen from U.S. Pat. Nos. 3,869,695 and 4,184,145. It has also been proposed to employ a resistance element embedded in a surface subject to wear so that the resistance element will wear with the surrounding surface. An example of such a wear sensor may be seen from published European patent application Ser. No. 0 077 206. The principal disadvantage of prior resistive-type devices is that the resistance material must be exposed to the same conditions as the surface of interest but will necessarily have a different wear rate when compared to that surface. Accordingly, inaccurate measurements will be obtained. Further, resistance-type wear sensors require the use of relatively complicated means for measuring the resistance of the sensor element and converting the resistance measurement into a percentage or other expression of wear.